Komunikasi Akustik Bawah Air dengan Time Reversal Menggunakan Filtered Multitone Modulation

Karena kanal multipath yang disebabkan dari time-reversal (TR) komunikasi akustik bawah air menggunakan single-carrier (SC) dengan modulasi tinggi berjumlah sangat banyak, maka akan menimbulkan adanya Intersymbol Interference (ISI). ISI yang disebabkan oleh multipath tersebut akan mengurangi kinerja proses TR sehingga perlu dihilangkan menggunakan adaptive equalizer. Dalam tugas akhir ini, metode komunikasi akustik TR menggunakan filtered multitone (FMT) modulation dimaksudkan untuk meningkatkan kinerja proses TR dengan mengurangi sisa ISI dalam sinyal yang diproses serta mengurangi kompleksitas adaptive equalizer untuk post-process. Modulasi FMT digunakan untuk memodulasi simbol informasi ke subcarrier terpisah dengan memanfaatkan bandwidth masing-masing subcarrier. Pada sistem ini menggunakan adaptive equalization dengan algoritma RLS yang ada pada penerima untuk menekan sisa ISI dan noise. Kinerja dari metode yang diusulkan ini dinilai melalui simulasi dan data real dari uji coba di kolam eksperimental. Uji coba ini dilakukan dengan variasi jarak 11 m, 40 m, dan 70 m. Hasil analisa TR menggunakan modulasi FMT pada jarak 11 m memiliki nilai BER sebesar 0.018 yang lebih kecil dibandingkan dengan TR menggunakan SC yaitu memiliki nilai BER sebesar 0.07. Hal tersebut menunjukkan bahwa performansi TR menggunakan modulasi FMT lebih baik daripada menggunakan modulasi SC. =================================================================================================== Since the multipath channel caused by the Time Reversal (TR) of acoustic communication underwater using a single carrier (SC) with high modulation are very numerous, then there will be Intersymbol Interference (ISI) . ISI that caused by the multipath will reduce performance of TR process, have to be eliminated using an adaptive equalizer. In this final project, the acoustic communication TIME Reversal method uses filtered multitone modulation (FMT) to improve performance time reversal method itself by reducing the remaining ISI and help reducing the complexity of the adaptive equalizer for the post process. FMT modulation is used to modulate information symbols into separate subcarriers. In this system it uses an adaptive equalization with existing RLS algorithm on the receiver to hold the rest of ISI and noise. The performance of the proposed method is assessed through simulations and real data from trials in experimental ponds. The trial was conducted with variations of distance of 11 m, 40 m, and 70 m. TR analysis trial result using FMT modulation at distance of 11 m has BER value equals to 0,018 which is lower compare to TR using SC that has BER value equal to 0.23. It shows that the performance of TR using FMT modulation is better than using SC modulation

Doctor of Philosophy

dissertationThe demand for high speed communication has been increasing in the past two decades. Multicarrier communication technology has been suggested to address this demand. Orthogonal frequency-division multiplexing (OFDM) is the most widely used multicarrier technique. However, OFDM has a number of disadvantages in time-varying channels, multiple access, and cognitive radios. On the other hand, filterbank multicarrier (FBMC) communication has been suggested as an alternative to OFDM that can overcome the disadvantages of OFDM. In this dissertation, we investigate the application of filtered multitone (FMT), a subset of FBMC modulation methods, to slow fading and fast fading channels. We investigate the FMT transmitter and receiver in continuous and discrete time domains. An efficient implementation of FMT systems is derived and the conditions for perfect reconstruction in an FBMC communication system are presented. We derive equations for FMT in slow fading channels that allow evaluation of FMT when applied to mobile wireless communication systems. We consider using fractionally spaced per tone channel equalizers with different number of taps. The numerical results are presented to investigate the performance of these equalizers. The numerical results show that single-tap equalizers suffice for typical wireless channels. The equalizer design study is advanced by introducing adaptive equalizers which use channel estimation. We derive equations for a minimum mean square error (MMSE) channel estimator and improve the channel estimation by considering the finite duration of channel impulse response. The results of optimum equalizers (when channel is known perfectly) are compared with those of the adaptive equalizers, and it is found that a loss of 1 dB or less incurs. We also introduce a new form of FMT which is specially designed to handle doubly dispersive channels. This method is called FMT-dd (FMT for doubly dispersive channels). The proposed FMT-dd is applied to two common methods of data symbol orientation in the time-frequency space grid; namely, rectangular and hexagonal lattices. The performance of these methods along with OFDM and the conventional FMT are compared and a significant improvement in performance is observed. The FMT-dd design is applied to real-world underwater acoustic (UWA) communication channels. The experimental results from an at-sea experiment (ACOMM10) show that this new design provides a significant gain over OFDM. The feasibility of implementing a MIMO system for multicarrier UWA communication channels is studied through computer simulations. Our study emphasizes the bandwidth efficiency of multicarrier MIMO communications .We show that the value of MIMO to UWA communication is very limited

SENSORY AND PERCEPTUAL CODES IN CORTICAL AUDITORY PROCESSING

A key aspect of human auditory cognition is establishing efficient and reliable representations about the acoustic environment, especially at the level of auditory cortex. Since the inception of encoding models that relate sound to neural response, three longstanding questions remain open. First, on the apparently insurmountable problem of fundamental changes to cortical responses depending on certain categories of sound (e.g. simple tones versus environmental sound). Second, on how to integrate inner or subjective perceptual experiences into sound encoding models, given that they presuppose existing, direct physical stimulation which is sometimes missed. And third, on how does context and learning fine-tune these encoding rules, as adaptive changes to improve impoverished conditions particularly important for communication sounds. In this series, each question is addressed by analysis of mappings from sound stimuli delivered-to and/or perceived-by a listener, to large-scale cortically-sourced response time series from magnetoencephalography. It is first shown that the divergent, categorical modes of sensory coding may unify by exploring alternative acoustic representations other than the traditional spectrogram, such as temporal transient maps. Encoding models of either of artificial random tones, music, or speech stimulus classes, were substantially matched in their structure when represented from acoustic energy increases –consistent with the existence of a domain-general common baseline processing stage. Separately, the matter of the perceptual experience of sound via cortical responses is addressed via stereotyped rhythmic patterns normally entraining cortical responses with equal periodicity. Here, it is shown that under conditions of perceptual restoration, namely cases where a listener reports hearing a specific sound pattern in the midst of noise nonetheless, one may access such endogenous representations in the form of evoked cortical oscillations at the same rhythmic rate. Finally, with regards to natural speech, it is shown that extensive prior experience over repeated listening of the same sentence materials may facilitate the ability to reconstruct the original stimulus even where noise replaces it, and to also expedite normal cortical processing times in listeners. Overall, the findings demonstrate cases by which sensory and perceptual coding approaches jointly continue to expand the enquiry about listeners’ personal experience of the communication-rich soundscape

WHOI acoustic telemetry project interim report 12/1/88 - 6/1/89

This interim report covers the progress of the acoustic telemetry project during the period 12/1/88 to 5/15/89. In general, the work followed the format specified in WHOI proposal No. 5674.1. The major exception was the deletion of the transmitter array development task and a corresponding funding decrease from $242,242 to$170,000. In addition, the period for the funding was extended to June 30, partly due to a two month delay in project startup. The telemetry project was centered around the construction, programming and testing of a digital receiver prototype capable of supporting future signal processing algorithms in real-time over ocean acoustic channels. The baseline receiver consists of a two-channel analog quadrature demodulator, and interface to a multiprocessor receiver for digital signal processing. The software developed includes routines for command and control of the analog demodulator, data handling and formatting, and minimal software to digitally implement an incoherent MFSK demodulator, synchronizer and data decoder. Data storage and display programs were also completed to facilitate the performance analysis of the unit during testing. The system was tested in Woods Hole harbor at data rates up to 4800 bits/sec. The acoustic channel was time-dispersive Rayleigh fading, and performance close to theoretical expectations was achieved. We are confident that the system error behavior is arising from channel-caused effects and known deficiencies in system performance, such as excessive synchronizer steady-state jitter.Funding was provided by the Office of Naval Research under contract Number N00014-86-K-0751, and by the Charles Stark Draper Laboratory Inc

Physiological and Behavioral Evidence of Auditory Processing Deficit in Children Suspected of Auditory Processing Disorder

A series of studies were carried out to examine the neural and behavioral processing of acoustic stimuli in children with suspected auditory processing disorder (sAPD). The click-evoked auditory brainstem responses recorded from children with sAPD and adults were analyzed using traditional clinical measures and detailed analysis seeking to explore the separate contributions of axonal conduction and synaptic transmission. Clinical measures revealed significant prolongation of absolute latencies and interwave intervals in children with sAPD compared to adults. Examination of responses delineating axonal vs. synaptic transmission showed frequent delays in synaptic factors and fewer instances of delays related to axonal conduction in children with sAPD compared to adults. Inefficient neural transmission in the auditory brainstem may lead to difficulty in coding of dynamic acoustic cues (envelope, fine structure or spectral shape) that are necessary for recognizing speech in quiet and in noise. The ability to use envelope and fine structure cues to recognize speech in noise was therefore examined in children with sAPD, typically developing children and adults. Typically developing children showed developmental trend in use of envelope cues. Whereas children with sAPD were less efficient in using envelope and fine structure cues to recognize speech in noise compared to age-matched children and adults. Perception of speech based on fine structure alone was difficult for both TD children and children with sAPD compared to adults. This could be due to developmental difficulty in integrating frequency information from different bands. Difficulty in integrating auditory filter outputs may lead to the inadequate representation of spectral shape, which is necessary for recognizing speech sounds. Spectral shape perception was assessed using a spectral ripple discrimination task in typically developing children, children with sAPD, and adults. Young children could resolve fewer of ripples per octave when compared older children and adults. The performance of children with sAPD was poor compared to age-matched controls and young adults. Spectral-ripple discrimination showed a strong trend for improvement in thresholds as a function of age in both typically developing children and children with sAPD. This suggests that spectral shape is a learned cue and may take a longer time to mature

Adaptive Modulation Schemes for Underwater Acoustic OFDM Communication

High data rate communication is challenging in underwater acoustic (UA) communication as UA channels vary fast along with the environmental factors. A real-time Orthogonal frequency-division multiplexing (OFDM) based adaptive UA communication system is studied in this research employing the National Instruments (NI) LabVIEW software and NI CompactDAQ device. The developed adaptive modulation schemes enhance the reliability of communication, guarantee continuous connectivity, ensure maximum performance under a fixed BER at all times and boost data rate